1. Field
The present disclosure relates to imaging optical systems and 3-dimensional (3D) image acquisition apparatuses, and more particularly, to imaging optical systems using one lens and one image sensor and 3D image acquisition apparatuses which are capable of acquiring a color image and a depth image at the same time by using the imaging optical system.
2. Description of the Related Art
Recently, with the development and the increased demand of 3D display devices displaying depth images, the importance of 3D content is being emphasized. Thus, 3D image acquisition apparatuses such as 3D cameras which are capable of directly producing 3D content based on user input are being researched. Such a 3D camera may acquire depth information together with existing 2D color image information through one photograph.
Depth information, which may be information related to a distance between surfaces of an object and a 3D camera, may be acquired by either a stereo vision method using two cameras or a triangulation method using structured light and a camera. However, it is difficult to acquire precise depth information through these methods because, as a distance between the object and the 3D camera is increased, the depth information is significantly decreased in accuracy. The depth information depends upon the surface state of the object.
To improve these limitations, a time-of-flight (TOF) technique has been introduced. The TOF technique is a method of measuring a TOF taken from a time period during which, after illumination light is projected onto an object, the illumination light reflected from the object is received by a light receiving unit. According to the TOF technique, light having a specific wavelength (for example, a near-infrared ray having a wavelength of about 850 nm) is projected onto a object by using an illumination optical system including a light emitting diode (LED) or a laser diode (LD). Then, the projected light is reflected from the object at the same specific wavelength and is received by a light receiving unit. Thereafter, a series of processes for extracting depth information, such as the modulation of the received light using a modulator having a previously known gain waveform, is performed. Various TOF techniques have been introduced according to the series of optical processing processes.
A 3D camera adopting the TOF technique includes an illumination optical system that emits illumination light for acquiring depth information and an imaging optical system for acquiring images of an object. The imaging optical system detects visible light reflected from the object to produce a general color image and simultaneously detects illumination light reflected from the object to produce a depth image having only depth information. Conventionally, the imaging optical system may separately include an objective lens and image sensor for detecting visible light and another objective lens and another image sensor for detecting illumination light (i.e., a 2-lens 2-sensor structure). However, in the 2-lens 2-sensor structure, a color image and a depth image have viewing angles different from each other. Thus, a separate process and applicable processing circuitry for matching the two images is required. As a result, the 3D camera may be increased in size, and also, manufacturing costs thereof may be increased.
Thus, a 3D camera including one common objective lens and two image sensors (i.e., a 1-lens 2-sensor structure) has been proposed. However, in the case of the 1-lens 2-sensor structure, visible light and illumination light are separated from each other, and thus are respectively transmitted to separate image sensors.